The TH04/TH05 BGM/SE mode setup is a good example for code where
different structure field offsets will vanish completely upon reverse-
engineering. If we continued to use the per-game ID string as the
variable name, we'd only have another game-specific "difference" there.
Part of P0065, funded by Touhou Patch Center.
… because TH04's version of this takes the ASCII stage ID directly from
the resident structure.
So boss battles are simply triggered by setting the background tile
scroll speed to 0? That means…
Funded by zorg.